TRB, Transportation Research Board Annual Meeting, WASHINGTON, ETATS-UNIS, 13-/01/2019 - 17/01/2019Due to a request to open the Normandy bridge in France to abnormal loads, some detailed investigations have been carried out on the current traffic loads, and on the expected fatigue lifetimes, with and without the abnormal loads. This long span cable-stayed bridge is made of a steel orthotropic deck, quite sensitive to fatigue under traffic loads. Using the simplest standardized fatigue load model of the Eurocodes (LM3 of Eurocode 1991-2) is much too conservative and leads to unrealistic calculated lifetimes of a few years. Therefore, a real traffic load assessment was performed with a Weigh-in-Motion (WIM) system. A bridge WIM (B-WIM) system has been installed on the bridge, and the traffic loads were measured continuously over 7 months. The influence lines of the most sensitive details, mainly at the welds between deck plate and longitudinal stiffeners, at various transversal locations, were re-calculated with a 3-D finite element model (FEM), and compared to former measured influence lines. Fatigue lifetimes were assessed using the Miner's law, using successively a simplified load model made of a standard tridem axle, the measured traffic loads on the Normandy bridge, some measured traffic loads on other French motorways, and finally with a superimposition of the current traffic loads and the expected abnormal loads. The transverse location of the wheels on the deck has a great influence on the fatigue damage. With all these results, pratical recommendations were delivered to the bridge concessionary about the acceptability of the abnormal loads
